Refrigeration system including refrigerant noise suppression



Oct. 6, 1970 DRURY ETAL 3,531,947

REFRIGERATION SYSTEM INCLUDING REFRIGERANT NOISE SUPPRESSION Filed 001;.29, 1968 INVENTORS FRANCIS M. DRURY &JERRY A. Pan: T

THEIR ATTORNEY United States Patent 3,531,947 REFRIGERATION SYSTEMINCLUDING REFRIGERANT NOISE SUPPRESSION Francis M. Drury and Jerry A.Priest, Louisville, Ky.,

assignors to General Electric Company, a corporation of New York FiledOct. 29, 1968, Ser. No. 771,464 Int. Cl. F251) 41/06 US. Cl. 62511 3Claims ABSTRACT OF THE DISCLOSURE A refrigeration system comprising inclosed series-flow relationship a condenser, a tubular flow restrictorand an evaporator includes means connecting the outlet end of therestrictor to the evaporator inlet for reducing the noise generated byrefrigerant flowing from the restrictor.

BACKGROUND OF THE INVENTION A well known refrigeration system includesin closed, series-flow relationship an evaporator, a compressor forWithdrawing refrigerant from the evaporator, a condenser for condensingthe refrigerant compressed by the compressor and tubular flow restrictormeans for controlling the flow of refrigerant to the evaporator. Thetubular flow restrictor means, commonly referred to as a capillary tube,maintains the desired pressure differential between the condenser andthe evaporator by restricting the flow of refrigerant therethrough andto this end its internal diameter is substantially less than theinternal diameter of the conduit forming the inlet end of theevaporator.

The refrigerant exiting from the flow restrictor may be in the form ofliquid or gas or a mixture of the two. Also as it exits fom the flowrestrictor a portion thereof usually vaporizes at the lower pressurecondition in the evaporator. The boiling turbulence resulting from thisvaporization as well as the exit velocity of the refrigerant, which isclose to sonic speed, constitute a major source of noise in theoperation of such a refrigeration system. This noise can be particularlybothersome in the operation of refrigeration systems such as thosecontained in room air conditioners. The usual means for isolating thissource of noise from the enclosure being conditioned has been to locatethe outlet end of the flow restrictor on the outdoor side of the usualpartition separating the room air conditioner into indoor and outdoorcompartments. This requires an additional unrestricted connecting tubefor connecting the outlet end of the flow restrictor to the inlet end ofthe evaporator which is positioned within the indoor compartment andresults in some cooling loss in the system.

SUMMARY OF THE INVENTION The present invention is directed to theprovision of means connecting the tubular flow restrictor with the inletend of the evaporator designed to control the flashing of liquidrefrigerant to gas in a manner such that the usual noises associatedwith this portion of a refrigeration system are substantially suppressedor eliminated.

To this end, there is provided in a refrigeration system comprising acondenser, a tubular flow restrictor and evaporator in closed seriesflow connection, improved means for connecting the outlet end of theflow restrictor to the inlet end of the evaporator made up of at leastthree sucessive tubular sections or segments of progressively increasingdiameters and decreasing lengths. In accordance with a preferred andcommercially practicable form of the invention, this connecting meanscomprises a series of telescoping interconnected tubular sections eachof which is a standard diameter refrigeration tubing with ice theinternal diameter of each succeeding tube being substantially equal ofthe external diameter of the preceding tubular section. The lengths ofeach section progressively decrease to provide a gradual flaring of theconnector in the direction of its outlet to the evaporator.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawing:

FIG. 1 is a schematic diagram of a closed refrigeration systemincorporating the present invention,

FIG. 2 is an enlarged sectional view of the connecting means formingpart of the refrigerating system of FIG. 1; and

FIG. 3 is a sectional view of an alternative form of connecting meansfor practicing the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. 1 of theaccompanying drawing, there is illustrated diagrammatically arefrigeration system including a compressor 1, a condenser 2, a tubularflow restrictor, such as a capillary tube 3-, the improved connectingmeans 4 of the present invention and an evaporator 5 connected in closedseries-flow relationship. In the operation of such a system, thecompressor 1 withdraws refrigerant vapor from the evaporator 5 anddischarges compressed refrigerant to the condenser 2. The high pressurerefrigerant condensed in the condenser 2 passes through the capillarytube 3 to the evaporator 5. The capillary tube 3 provides a substantialrestriction to the flow of liquid refrigerant to the evaporator andthereby maintains the desired range of pressure differential between thecondenser and the evaporator in a well known manner.

To maintain such pressure differential, the internal diameter of thecapillary tube 3 is substantially smaller than the remaining fluidpassages in the refrigeration system including the inlet end 6 to theevaporator 5. In previously known refrigeration systems of this typesuch as those specifically used in room air conditioners, the outlet endof the capillary tube 3 was connected directly to the inlet end 6 of theevaporator, or to a suitable non-restrictive tubular connection havingsubstantially the same diameter as the evaporator tubing or conduit,employing suitable means for plugging the space between the outersurface of the capillary and the inner surface of the evaporator inlet.With such a direct connection, the refrigerant in the form of either aliquid or a gas or mixture thereof issued from the outlet end of therelatively small capillary at a relatively high velocity close to sonicspeed. Also as this refrigerant exited from the capillary tube to thelarger diameter evaporator conduit operating at compressor suctionpressures, some of the liquid refrigerant flashed into gas at this lowerpressure resulting in a turbulent and noise producing flow at the inletto the evaporator. This noise may be described as a roaring sound,accompanied in some cases believed to result from the use of a condenserwhich alternately feeds gas and liquid slugs to the capillary, by arelatively loud popping sound similar to that of popping corn.

Both the roaring noise and the popping noise are substantiallyeliminated in accordance with the present invention by employing aconnector between the capillary outlet and the evaporator inlet which inits preferred form comprises a plurality of telescoping tubular segmentsor sections, the first of which has an inner diameter approximatelyequal to the outer diameter of the capillary and each succeeding sectionbearing a similar relationship to the preceding one. Generallycommercially available refrigerant tubing of various sizes can beemployed in manufacturing the connector.

For optimum results, the effective lengths of the individual segments orsections of the connector are such that the connector provides a gradualtransition from the inner diameter of the capillary to the innerdiameter of the evaporator inlet. To this end, at least three tubularsections or in other words three steps in the expanding connector arerequired for the desired suppression of the above mentioned noises.

Also, for best results, the wall thicknesses of all the segments orsections are substantially equal and this criterion is satisfied by thefact that most commercially available refrigerant tubing within therange of sizes employed for making the connector have about the samewall thicknesses.

Broadly described, the lengths of the individual segments or sectionsare selected to provide an increase in the cross sectional area of theconnector from capillary to the evaporator inlet at a logarithmic ratewith the lengths of the successive segments being determined by theformula X log N +1 where X is a multiplier between 8 and 12, preferably10, and N is the number of the section in the connector. In other words,the lengths of the segments of the connector are successively determinedby the progressive formulas X log 2; X log 3; X log 4; etc.

In accordance with the above equations, the value of X determines theaverage rate of increase in cross sectional area within the connector.Tests have indicated that if X is a number substantially less than 8,there is no substantial elimination or repression of the roaring andpopping noises whereas if X has the value greater than 12 the rate ofincrease in the effective cross sectional area of the connector is sogradual that the first section or sections of the connector effectivelyincrease the capillary length and hence result in an undesirableincrease in the pressure differential between the high and low pressuresides of the system.

A typical example of a preferred connector for the practice of thepresent invention is illustrated in FIG. 2 of the drawing. Thisconnector was designed to provide an optimum noise suppression withsubstantially no increase in back pressure in a system comprising acapillary tube having an exterior diameter of about 0.125 inch and anevaporator inlet having an exterior diameter of 0.375 inch and aninterior diameter of 0.319 inch. Each of the segments employed inmanufacturing this connector had a will thickness of about 0.028 inch orin other words a difference of about 0.056 inch between the inner andouter diameters thereof. More specifically the first section 8 had a Aouter diameter, the second section 9 a A1" outer diameter and the thirdsection 10 an outer diameter of The exterior diameter of the thirdsection was such that it approximately matched the interior diameter ofthe evaporator inlet 6.

Employing the above formula with X equal to the preferred multiplier 10,the effective lengths of the individual segments (with the insertiondepth of each segment into a succeeding segment being extra), were asindicated on the drawing. The first segment 8 was 3" in length, thesecond segment 9 was 1.75 in length and the third segment 1.2" inlength.

This connector has been extensively employed in a room air conditionersystem and has substantially suppressed or eliminated all of thecapillary-evaporator joint noise. It is easily manufactured merely bysoldering or brazing the overlapping portions of the respectivesegments. The ledges or steps formed by the outlet end of each of thesegment do not appear to provide any significant noise problempresumably because the refrigerant flows through the connector in such amanner that its boundary layers tend to smooth out these irregularities.

In manufacturing some connectors, it may be advantageous to manufacturesome adjacent segments from a single piece of tubing as for example byswagging a portion thereof to a smaller diameter. Such a connector isshown in FIG. 3 in which the first two segments 11 and 12, correspondingto segments 8 and 9 of FIG. 2, are made by reducing the cross sectionalarea of a piece of tubing having the internal diameter of the section 12to a smaller diameter section 11.

It has also been found that the subject connector is particularly usefulfor solving field complaints concerning abnormal refrigerant noises inair conditioning systems.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a refrigeration system including a condenser, an evaporator havinga tubular inlet and a tubular flow restrictor for controlling the fiowof refrigerant from said condenser to said evaporator and having a flowrestriction sufficient to maintain the desired range of pressure differential between said condenser and said evaporator;

means for connecting the outlet end of said flow restrictor to saidevaporator inlet;

said connecting means comprising at least three successive tubularsections of progressively increasing diameters and decreasing lengthsfrom said flow restrictor to said evaporator inlet for reducing thenoise generated by the refrigerant flowing from said flow restrictor;

the effective lengths of said sections being determined by the formula Xlog N +1 wherein X is a number between 8 and 12 and N is the number ofthe section in said connector.

2. The system of claim 1 in which the wall thickness of said sectionsare each substantially equal to the Wall thickness of said flowrestrictor.

3. The system of claim 1 in which X is equal to approximately 10.

References Cited UNITED STATES PATENTS 2,434,118 1/1948 Newman 62--5l1MEYER PERLIN, Primary Examiner

